This invention relates to a method for producing silicon nitride powder.
A silica reducing method is a publicly known method for producing pure silicon nitride powder at a low cost in which a mixture of silica powder and carbon powder is heated in a nitrogen atmosphere. For example, Japanese Patent Publication No. 54-23917 discloses a method of producing silicon nitride powder in which silica powder and carbon powder are mixed with at least one silicon compound selected from the group of silicon nitride powder, silicon carbide powder and silicon oxi-nitride powder and then heated in an atmosphere containing nitrogen gas in such a way that a reducing nitriding reaction may occur.
According to such a conventional method, the produced silicon nitride powder is apt to contain a relatively large content of carbon.
As well-known, the content of carbon contained in the silicon nitride powder should be decreased in order to obtain a dense sintered body.
On the other hand, Japanese Patent Publication No. 57-44602 discloses a method for reducing and nitriding silica in a mixed gas atmosphere including hydrocarbon gas, ammonia gas and hydrogen gas. According to this conventional method, decomposition of NH.sub.3 is restrained by the hydrogen gas which is mixed with the other gases so that Si.sub.3 N.sub.4 synthesis reaction is retarded.